Electrostatic precipitating method

ABSTRACT

An electrostatic precipitating method which includes moving a gas stream with charged particles entrained therein along a prescribed path and imposing an electrostatic force field on the charged particles with a first component of force exerted on the particles opposite to the direction of movement of the particles to slow the particles down and a second component of force exerted on the particles generally normal to the path of movement of the particles to separate the particles from the gas stream.

United States Patent [191 Huang et al.

[ Sept. 23, 1975 ELECTROSTATIC PRECIPITATING METHOD [76] Inventors: A.Ben Huang, 3134 Woodrow Way, NE, Atlanta, Ga. 30319; Arnold L. Ducoffe,3544 Paces Ferry Rd., N.W., Atlanta, Ga. 30339 [22] Filed: Oct. 11, 1973[21] Appl. No.: 405,419

Related US. Application Data [62] Division of Ser. No. 249,167, May 1,1972, Pat. No.

[52] US. Cl. 55/4; 2l/D1G. 2; 23/260; 23/277 C; 23/284; 55/5; 55/11;55/13;

55/114; 55/117; 55/121; 55/129; 55/131;55/135;55/138;55/146;55/155;55/D1G. 38; 204/l57.1 R; 250/527; 250/432;423/52;

[51] Int. CI. 803C 3/74; B03C 3/88 [58] Field of Search "SS/ 2,4, l1,12, 13, 101, 55/108,113,114, 120,121, 131, 136, 137,

138, 154, 155, 5, 117, 129, 135, 146, DIG.

157.1 HE, 158, 158 HE; 250/527, 428, 432,

R, 55, 74 R, 74 A, 102, DIG. 2

[56] References Cited UNITED STATES PATENTS 2,225,677 12/1940 White55/129 X m ZZ 2,249,801 7/1941 White 55/129 X 2,759,877 8/1956 Eron208/161 X 3,370,646 2/1928 Hopper i 165/95 3,616,606 11/1971 Vincent55/138 X 3,650,092 3/1972 Gourdine et al 310/11 X 3,681,896 8/1972Velkoff 62/71 X 3,718,029 2/1973 Gourdine et 324/71 PC 3,733,784 5/1973Anderson ct al. 55/341 X FOREIGN PATENTS OR APPLICATIONS 92,636 5/1923Austria 55/131 698,874 10/1953 United Kingdom 959,655 6/1964 UnitedKingdom 55/131 Primary Examiner-Dennis E. Talbert, Jr. Attorney, Agent,or Firm-B. .1. Powell [57] ABSTRACT An electrostatic precipitatingmethod which includes moving a gas stream with charged particlesentrained therein along a prescribed path and imposing an electrostaticforce field on the charged particles with a first component of forceexerted on the particles opposite to the direction of movement of theparticles to slow the particles down and a second component of forceexerted on the particles generally normal to the path of movement of theparticles to separate the particles from the gas stream.

7 Claims, 13 Drawing Figures US Patent Sept. 23,1975 Sheet 1 Of33,907,520

US Patent Sept. 23,1975 Sheet 2 01 3 US Patent Sept. 23,1975 Sheet 3 of33,907,520

ELECTROSTATIC PRECIPITATING METHOD CROSS-REFERENCE TO RELATEDAPPLICATIONS This application is a division of our copending applicationSer. No. 249,167, filed May I, 1972 entitled Electrostatic PrecipitatingApparatus and Method, now U.S. Pat. No. 3,782,905.

BACKGROUND OF THE INVENTION Electrostatic precipitators are available onthe market today. These prior art precipitators first charge theentrained particulate matter in a gas stream and then separate thethusly charged particles by passing the gas stream with the chargedparticles therein through a series of charged members or grids imposedin the stream path. All of these precipitators collect the separatedparticles on the oppositely charged members or grids. This causes thecollecting efficiency of the grids to quickly lose their collectingability due to the insulation formed by the collected particles andrequires a greater grid potential to maintain operation. Attempts havebeen made to solve this problem by intermittently preventing the gasstream from flowing across the grid and rapping the grid to dislodge theparticles therefrom so that gravity will cause the particles to fallfrom the grid to be collected. This not only prevents the desirablecontinuous full operation of the precipitator but also does notcompletely clean the grid, thus reducing the effective operational timebefore the grids must be again rapped.

Because of the inefficiency of such prior art precipitators, attemptshave been made to mechanically slow down the movement of the particleswithin the precipitator by creating highly turbulent zones in the gasstream within the precipitator to form eddies which entrap theparticles. In order to create sufficient turbulency to significantlyincrease the particle collection capability ofthe precipitator, a backpressure is created requiring more power to force the gas stream throughthe precipitator and thus increase the cost of operating same.

SUMMARY OF THE INVENTION These and other problems and disadvantagesassociated with the prior art are overcome by the invention disclosedherein by providing an electrostatic precipitating apparatus and methodwhich separates the particles from a gas stream without collecting theparticles on the primary field producing grids within the stream path sothat operation is continuous. Moreover, the invention creates minimumback pressure in the stream to minimize the power required to force thegas stream through the invention. Also, because the particles are notcollected on the grids within the gas stream the electrical fieldgenerating power is maintained at a minimum. Moreover, the apparatus ofthe invention is extremely simple thereby minimizing the constructionand installation cost thereof.

The apparatus of the invention includes a duct through which the gasstream is forced, charging means for charging the particulate matter inthe gas stream, and separating means for separating the chargedparticulate matter from the gas stream. Converter means may be providedfor converting gaseous pollutants into particulate pollutants forseparation.

One embodiment of the separating means includes an entry grid with acharge of opposite polarity to the charge on the particulate matter andan exit grid downstream of the entry grid with a charge of like polarityto the charge on the particulate matter. At least a portion of the ductwall between the entry and exit grids is charged like the entry grid! toprovide a collecting surface onto which the particulate matter isdeposited. This is because an electrostatic field is generated betweenthe entry and exit grids and the portion of the duct wall with a chargethereon which exerts a resultant force on the charged particles whichhas a major component of force contra to the direction of gas flow and aminor component of force normal to the direction of gas flow and towardthe charged portion of the duct wall.

Additional exit grids may be spaced from each other downstream of theentry grid. The first downstream exit grid is charged to a firstpotential of like polarity to the charged particles, the seconddownstream grid is charrged to a second potential of like polarity tocharged particles but higher than the first potential. the third grid ischarged to a third potential of like polarity to the charged particlesbut higher than the second potential, etc. Thus. each exit grid has ahigher potential than the next upstream exit grid to generate anelectrostatic force field between each pair of adjacent grids thatimposes a force on the charged particles contra to the direction of gasflow.

These and other features and advantages of the invention will becomemore apparent upon consideration of the following specification andaccompanying drawings wherein like characters of reference designatecorresponding parts throughout the several views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinalcross-sectional view of one embodiment of the invention;

FIG. 2 is a cross-sectional view taken along line 22 in FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 33 in FIG.2;

FIG. 4 is a cross-sectional view taken along line 44 in FIG. 1;

FIG. 5 is a top view of the invention of FIG. 1 showing a wall cleaningmechanism.

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 5;

FIG. 7 is a cross-sectional view showing a second embodiment of theseparating means of the invention;

FIG. 8 is a crosssectional view taken along line 8-8 in FIG. 7;

FIG. 9 is a longitudinal cross-sectional view of a modified form of theseparating means shown in FIG. 7;

FIG. 10 is a longitudinal cross-sectional view showing a thirdembodiment of the separating means of the invention;

FIG. 11 is a front elevational view showing an alternate form of thegrid construction;

FIG. 12 is a cross-sectional view taken along line l2l2 in FIG. 11showing modification of the grid shown in FIG. 11; and,

FIG. 13 is a free body diagram illustrating the forces on one of theentrained charged particles in the gas stream as it passes through theseparating means.

These figures and the following detailed description disclose specificembodiments of the invention, however, the inventive concept is notlimited thereto since it may be embodied in other forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Referring to thefigures, the apparatus of the invention includes generally a duct 10, aconverter 11 for converting gaseous pollutants in a gas stream passingthrough the duct into particulate matter, a corona discharge unit 12downstream of the converter 11 for charging the particulate matterentrained in the gas stream, and a separating section downstream of thecorona discharge unit for separating the charged particulate matter fromthe gas stream. The first embodiment of the separating section isdesignated 100, the second embodiment is designated 200, themodification of the second embodiment is designated 300, and the thirdembodiment is designated 400.

Referring to FIG. 1, the duct 10 is illustrated with a circularcross-section but may have other configurations such as the squarecross-section illustrated in FIGS. 7-9. The gas stream is forced ordrawn through duct 10 by an external pumping means (not shown) as iswell known in the art.

The converter 11 is placed within the passage 14 through duct 10adjacent the entry end 15 thereof which receives the gas streamcontaining pollutants therein. The pollutants in the gas stream areusually in both gaseous form and in particulate form. The converter 11converts the gaseous pollutants into a particulate form. Particulate asused herein means both solids and liquid droplets since both may beelectrostatically charged for separation. While it is understood thatmany pollutants may be found, normally sulfur dioxide, carbon monoxide,and nitrogen oxides are found in exhaust gases in a gaseous form whilecarbon particles are normally found in particulate form. The converter11 is used to convert the pollutants in gaseous form into particulateform by injecting a converting medium into the gas stream.

The converter 11 may have several configurations but is shown in FIG. 1as a series of concentrically arranged pipes 16 located in passage 14 ofduct 10 connected to a medium source 18 through a pump 19 and manifold20. A plurality of nozzles 21 are provided on each pipe 16 for injectingthe converting medium from source 18 into the gas stream entering theduct 10. While the nozzles 21 are illustrated as facing downstream, itis to be understood that they may be made to face upstream. It is alsoto be understood that the converting medium may be different for eachgaseous pollutant to be converted and there may be a set of pipes 16 foreach converting medium to be used or the converting mediums may beinjected from a single set of pipes 16. Various converting mediums maybe used, however, a list of possible mediums to be used are set forth inTable I hereinafter. The list of mediums shown in Table I is in no waymeant to be all inclusive. Thus, thegas stream issues from the converterwith all of the pollutants to be separated entrained in the gas streamas particulate matter ready for ionization.

The gas stream then passes through the corona discharge unit 12 ofconventional construction. While various configurations may be used, aconventional platewire arrangement 22 is illustrated. The unit 12 maycharge the particulate matter in the gas stream either positively ornegatively, however, it has been found that a sufficient charge will beimposed on the particulate matter when a voltage of 20,000 volts isimposed on the plate-wire arrangement 22. Thus, the gas stream exits thecorona discharge unit 12 with the particulate matter entrained thereincharged.

The first embodiment of the separating section is shown in FIGS. 1-4,and includes an entry grid 101 and an exit grid 102 spaced a prescribeddistance L apart. The entry grid 101 is oppositely charged with respectto the charge on the particulate matter, here shown as grounded, whilethe exit grid 102 is charged the same as the charge on the particulatematter. Oppositely charged or opposite polarity as used herein includesa charge with unlike polarity or grounded. Thus, while the entry gridsand duct walls are illustrated herein as grounded, they could have ahigh voltage of unlike polarity imposed thereon. The section 104 of duct10 between the grids 101 and 102 has its side wall 105 oppositelycharged like entry grid 101 or grounded as seen in the figures. Thus,when the grids 101 and 102 and side wall 105 are powered, anelectrostatic force field will be established between the grids 101 and102 and side wall 105 that will exert a force on the charged particulatematter entrained in the gas stream opposite to the direction of gas flowand normal to the direction of gas flow to separate the chargedparticulate matter from the gas stream and deposit same on the insidesurface 107 of the side wall 105.

Referring now more specifically to FIGS. 2 and 3, the entry grid 101includes a plurality of concentric conductor rings 106 carried on thedownstream side of a plurality of radially extending circumferentiallyspaced support ducts 108 made of an insulating material. The rings 106are arranged in a plane perpendicular to the path P of gas flow throughthe duct 10. A plurality of concentrically arranged annular ducts 109also made of an insulating material extend between and are connected tothe radial ducts 108 on the upstream side of the conductor rings 106.The annular ducts are hollow and are provided with an open mouth 110 onthe downstream side thereof which is wider than the rings 106 and withinwhich the rings 106 are positioned as seen in FIG. 3 to provide anannular opening 111 on both sides of the rings 106 which communicateswith the cavity 112 within the annular duct 109. Thus, the annular ducts109 completely cover the upstream side of the conductor rings 106 aswell as the edges thereof. The rings 106 may be recessed within theannular ducts 109 to insure passage of the charged particulate matterpast the conductor rings 106 before they are attracted toward the rings106 as will become more apparent.

The internal passage in the radial ducts 108 is connected to apressurized clean air source 114 and communlcates with the cavities 112in the annular ducts 109 so that the clean air enters through thepassage in the ducts 108, passes through the cavities 112 and isdischarged around the conductor rings 106 through the annular openings111. This further insures passage of the charged particulate matterdownstream of grid 101 before they are attracted toward rings 106 aswill become more apparent. The rings 106 are grounded so as to beoppositely charged with respect to the charge on the particulate matter.

As best seen in FIGS. 1 and 4, the exit grid 102 includes a plurality ofannular wire rings mounted on a diametrically extending insulatedsupport 121 so that rings 120 are concentric and lie in a planeperpendicular to the path P of the gas flow. The rings 120 are connectedto a voltage source 122 so that the rings have a potential imposedthereon of the same polarity as the charge on the particulate matter.Because the side wall 105 is grounded like the rings 106, anelectrostatic force field F is set up between the grids 101 and 102 andbetween the grid 102 and side wall 105 which exerts a resultant forcefoneach particle of the charged particulate matter which has a first majorcomponent f,. directed oppositely to the direction of gas flow to retardthe downstream movement of the particle and a second component of forcef which is directed radially outwardly with respect to the duct todirect the particle toward the nearest portion of the side wall 105 aswill become more apparent.

Because the charged particles are deposited on the side wall 105, meansmay be provided for cleaning the inside surface 107 of the side wall 105without interrupting the gas flow through the separating section 100.One specific embodiment of such a cleaning mechanism is shown in FIGS. 5and 6 and is designated 130. Since many embodiments may be devised, thismechanism 130 is shown for illustrative purposes only. The cleaningmechanism 130 is shown in FIGS. 5 and 6 and includes a cylinder 131which has a plurality of side walls 105 equally spaced about the centerof rotation of cylinder 131 so that any one of the side walls 105 may bepivoted into registration with the rest of duct 10. The cylinder 131 isrotatably mounted by a shaft 132 adjacent the duct 10 so as to allow theside walls 105 to be selectively moved into alignment with the rest ofthe duct 10. An indexing motor 134 is connected to shaft 132 so as .toallow the side walls 105 to be placed in registration with the duct 10.A cleaning brush 135 driven by motor 136 is mounted on a car riage 138diametrically opposite the duct 10 so that when the duct 10 is inregistration with one of the side walls 105, the brush 135 will be inregistration with another of the side walls 105. Brush 135 can berotated by motor 136 and traversed along the carriage 138 so as to beinserted within the side wall 105 in registration therewith to cleansame. Appropriate washing means (not shown) may be provided for insuringthat the particulate pollutants on the inside surface of the side wall105 will be removed as a result of the brushing action. It will also benoted that the side walls 105 are arranged closely adjacent to eachother so that when the cylinder 131 is indexed by the motor 134, gasflow through the duct 10 will not be appreciably interrupted to providefor continuous operation in.-section 100.

FIGS. 7 and 8 illustrate the second embodiment 200 of the separatingsection. It will be understood that the second embodiment 200 will beused to replace the first embodiment 100 in the duct 10 and since theconverter 11, and the corona discharge unit 12 remain the seame, theyare omitted from these views for sake of simplicity. It will be notedthat the duct 10 illustrated in the second embodiment 200 of theseparating section has a square cross-section rather than a circularcross-section as illustrated for the first embodiment of the separatingsection.

The separating section 200 includes an entry grid 201 and an exit grid202 spaced a prescribed distance L apart. The entry grid 201 is the sameas the entry grid 101 for the first embodiment 100 of the separatingsection and is oppositely charged with respect to the charge on theparticulate matter or grounded shown herein since the particulate matterhas a charge of a prescribed voltage thereon. It will be noted. however,that the grid 201 has a square configuration rather than a circularconfiguration like the grid 101, but. the functional arrangement of thegrid 201 is the same as the grid 101.

The exit grid 202 is similar to the grid 102 with a plurality of annularwire rings 220 mounted on a diametrically extending insulated support221 so that the rings 220 are concentric with each other and lie in aplane perpendicular to the path of "the gas flow. It will be noted thatthe rings 221 are arranged in a configuration like the crosssection ofthe duct 10 and are thus in the shape ofa square as illustrated in FIGS.7 and 8. In addition, a plurality of secondary conducting members 225are provided along the upper edge of the grid 202 and are equally spacedfrom each other and from the rings 220. The members 225 are positionedon that side of the exit grid 202 toward the entry grid 201 as willbecome more apparent. The rings 220 and the members 225 are connected toa voltage source 222 so that the rings and members have a potentialimposed thereon of the same polarity as the charge on the particulatematter.

The section 200 has a side wall 205 extending be tween the grids 201 and202 with a generally square tubular cross-section. The side wall 205 hasan opening 206 in the bottom portion thereof under which is posi tioneda grounded collector member 230 which is insulated from side wall 205.While the collector member 230 may have any of a number of differentconfigurations, the member 230 illustrated is a flexible conductive beltmounted on rolls 231 closely adjacent the opening 206 and lying outsideof the side wall 205. A cleaning member 232 is positioned at one end ofthe member 230 so as to clean the deposited particulate matter therefromas the flexible member is indexed on the rolls 231. An appropriatemechanism (not shown) is provided for indexing the member 230periodically to selectively clean the deposited particulate mattertherefrom. It is to be further understood that the side wall 205 may beinsulated from the rest of the duct 10 and grounded similarly to that ofsection 100.

Since the member 230 is grounded, it will be seen that when the voltageof the same polarity as that on the particulate matter is imposed on therings 220 and members 225 of the exit grid 20 2, an electrostatic forcefield F is set up between the grids 201 and 202 and between the grid 202and the grounded collecting member 230. The force field F exerts aresultant force fon each particle of the particulate-matter which has afirst major componentfl. directed oppositely to the gas flow to retardthe downstream movement of the particle and a second component of forcefdirected downwardly perpendicular to the direction of gas flow to forcethe charged particle toward the collection member 230. Thus, it will beseen that the particulate matter in the gas stream will be collected onthe collection member 230 and then the collection member 230 can beselectively indexed when the particulate matter collected thereon hasbuilt up to a prescribed amount. Because the particulate matter iscollected on one side of the side wall 205, it will be seen that thecollected particulate matter can be easily disposed of.

Referring now to FIG. 9, the modification designated 300 of the secondembodiment of the separating section is illustrated. Since the converter11 and discharge corona unit 12 remain the same, they are omitted,however, it is to be understood that they could be used in combinationwith this embodiment of the separating section 300. The section 300includes generally an entry grid 301 and an exit grid 302 mounted withinthe side wall 305 of duct 10. It will be noted that the plane of theentry grid 301 is arranged at an angle a with respect to the path P ofthe gas flow in the vertical direction and perpendicular to the path Pin the other direction. The exit grid 302 is arranged at an angle B withrespect to the path P of the gas flow in the vertical direction andperpendicular to the path P in the other direction. The angles a and Bmay be varied to meet the particular requirements of each individualapplication.

The entry grid 301 is of the same construction as the entry grid 101 inthe section 100 except that the arrangement of the insulating ducts 309and conductor rings 306 are revised to a generally square configurationto match the square configuration of the duct illustrated and modifiedso that the vertical spacing between the rings 106 is equal. Likewise,the exit grid 302 is similar to the exit grid 102 of the section 100except that the rings 302 are arranged to conform to the squareconfiguration of the side wall 305 and that the spacing between therings 320 are equal in a vertical plane. The bottom portion of the sidewall 305 is provided with an opening 306 like the opening 206 and acollection member 330 is positioned thereunder like the member 230 sothat the charged particulate matter can be collected thereon.

The entry grid 301 and the collection member 330 are connected to groundand the exit grid 302 is connected to the voltage source 332 to chargethe exit grid with a potential of the same polarity as the charge on theparticulate matter. Thus, it will be seen that an electrostatic forcefield F is established between the entry grid 301 and the exit grid 302and the exit grid 302 and the collection member 330 so that a resultantforce fis imposed on the charged particles of the particulate matterwithin the section 300 which has a first component fi. directedoppositely to the direction of gas flow and a second component f,, whichis directed downwardly toward the collection member 330 normal to thepath P of the gas flow. Therefore, the charged particles of theparticulate matter entering the section 300 will be displaced downwardlyand onto the collection member 330 to separate the particulate matterfrom the gas stream. The collection member 330 may be indexed asspecified for the separating section 200 to remove the collectedparticulate matter therefrom.

The third embodiment 400 of the separating section is illustrated inFIG. 10. In this embodiment, an entry grid 401 is provided and aplurality of exit grids 402 are also provided. While any number of exitgrids may be used in the section 400, three are illustrated and aredesignated 402,,, 402,, and 402,.. The grids 401 and 402 are arranged soas to lie in a plane perpendicular to the direction of the gas flow withthe entry grid 401 having the same configuration as the entry grid 101because the side wall 405 is of a circular cross-section. Likewise, eachof the exit grids 402,,402,. have a configuration similar to theconfiguration of the exit grid 102 of the first embodiment 100 of theseparating section. The exit grid 402,, is spaced a prescribed distanceL from the entry grid 401, the exit grid 402,, is spaced a prescribeddistance L from the exit grid 402,, and the exit grid 402, is spaced aprescribed distance L" from the exit grid 402,,. While various distancesL, L or L may be used, they are illustrated as equal in FIG. 10, itbeing understood that these distnaces are dependent upon the diameter dof the duct 10. The entry grid 401 is grounded as with the otherembodiments of the invention, the exit grid 402,, is charged to a firstpotential V, of the same polarity as the charge on the particulatematter, the second exit grid 402,, is charged to a second potential Vwhich is greater than the potential V on the grid 402,,. The next exitgrid 402, is charged to a potential V which is greater than thepotential V on the grid 402,,. Thus, there will be a first force field Fset up between the entry grid 401 and the first exit grid 402,, whichexerts a resultant component of forcefon each particle of the chargedparticulate matter which is directed oppositely to the direction of thegas flow. Likewise, a second electrostatic force field F will be set upbetween the grids 402,, and 402,, which also exerts a component forcef,on the particles of the particulate matter which is opposite to thedirection of the gas flow. Also, an electrostatic force field F will beset up between the grids 402, and 402,. that exerts a component of forcef on the particles of the particulate matter which is directedoppositely to the direction of the gas flow. Thus, as the particulatematter progresses through the section 400, the particles have a forceexerted thereon which is constantly and oppositely directed to thedirection of the gas flow. Because there is a natural self-repulsoinforce between the particles of the particulate matter as a result of allof the particles having like charges thereon, this self-repulsion forcewill tend to displace the particles toward the side walls within thesection 400 thus separating them on the side wall 405 as the particlesmove through the section 400. To further enhance the separation of theparticles from the gas stream. the side wall 405 may be grounded asillustrated for the other embodiments of the separating section to causethe particles to be deposited thereon. Likewise, the grids 401 and 402may be arranged to cause the particles to be separated in a singledownwardly direction as illustrated in FIGS. 7-9.

Referring to FIGS. '11 and 12, an alternate embodiment of the entry andexit grids is illustrated and designated 500. The grid 500 is a plate501 having a configuration corresponding to the cross-sectionalconfiguration of duct 10 having a plurality of punched openings 502therethrough to leave narrow ribs 504 in place 501. To allow use of thegrid 500 as an entry grid a thin insulating coating 505 of knownmaterial may be used to cover the upstream facing side of plate 501 andthe edges of the openings 502 as seen in FIG. 1. To make an exit grid,the coating 505 is omitted. The grid S00 is substituted for the gridsdescribed hereinbefore and serves the same function.

OPERATION In operation, it will be seen that the polluted gas stream isforced or drawn through the duct 10 along the path P. If the pollutedgas stream contains gaseous pollutants as is generally the case withexhaust gases, the stream first passes through the converter 11. Theconverting medium is injected into the gas stream whereupon the mediumreacts with the gaseeous pollutants to form particles. Because differentmediums may be used for each type of gaseous pollutant or for differentpollutants, it is to be understood that more than one injection unit,here shown as pipes 16 and nozzles 21, may be necessary to obtainconversion of all of the gaseous pollutants. Also because the convertingmedium itself may be in a gaseous, liquid or solid state, it may benecessary to modify the converter to inject the particular medium.However, it is to be understood that such modification is within thescope of the invention.

When the gas stream is exhaust gases from a power source such as factoryor electrical power plants or in ternal combustion engines, theconverting medium may be selected from those identified in Table Iattached hereinafter.

For example, sulfur dioxide (S may be converted into solid particulatematter by injecting ammonia (NH from nozzles 21 or injecting calciumoxide (CaG) or maganese dioxide (MnO in powder form through nozzles 21.Heating coils HC may be placed in duct to assist in heating the gasstream for better reaction. The nitrogen dioxide (N0 may be convertedinto an aerosol containing both liquids and solids by injecting one ofthe cyclic olefin compounds such as ethylene from nozzles 21. Anultraviolet source US, here shown as a sun lamp but may be a mercuryarc, may be provided for enhancing the reaction speed. The nitric oxide(NO) can first be converted to nitrogen dioxide by the injection or airor oxygen (0 and then converted as above described.

Carbon monoxide, on the other hand, can be converted into harmlesscarbon dioxide (CO by the injection of air or oxygen (0 as is well knownespecially if the gas stream is heated by coils HC. Also, the carbonmonoxide can be converted by injecting lead chloride combined with waterPbCl H O with the lead being removed by the separating sections. It mustalso be noted that converter 11 may not be necessary if only particulatematter already in the gas stream is to be removed.

After the gas stream exits the converter 11 it enters the coronadischarge unit 12 as it moves along path P in duct 10. The unit 12operates in known manner to charge the particles in the gas stream to apredetermined level with a particular polarity. The plate-wirearrangement 22 has either the plate or wire grounded in conventionalmanner with either a positive or negative polarity potential imposed onthe ungrounded plate or wire. Thus if a positive polarity potential isimposed thereon, it will be seen that the particles passing therethroughwhile entrained in the gas stream will have a resulting positive chargeimposed thereon while a negative polarity potential will impose anegative charge on the particles.

It is also to be understood that some of the particles within the gasstream may more readily accept a charge thereon of either a positivepolarity or negative polarity. If such is the case, it may be necessaryto have a first corona discharge unit 12 for imposing a charge on theparticles of one polarity and the gas stream passed through theseparating section 100, 200, 300 or 400 to separate those particleswhich have accepted a charge. The gas stream can thereafter be passedthrough a second corona discharge unit 12 to impose a charge on theremaining particles of the other polarity and the gas stream passedthrough a second separating section 100, 200, 300 or 400 to separate theremaining particles.

Referring to the free body diagram as best seen in FIG. 13 of aparticular charged particle P, of the particulate pollutant matter inthe gas stream as it issues from the corona discharge unit 12, it willbe seen that the gas stream exerts a force F on the particle Pp due toits entrainment gene ally parallel to the path P of movement of the gasstream through the duct 10. This path P is horizontal as seen in thefigures. however, it is to be understood that path P could be at otherpositions such as vertical. Also forces F will be exerted on theparticle Pp by the self-repulsion between particles due to their chargesof like polarity. Because the outside layer of particles Pp adjacent theside wall of the duct 10 has no repulsion with respect to the side wall.there will tend to be a general drift of the particles Pp toward theside wall. There will also be a gravitational force FM acting on theparticle P however, such force is generally insignificant in theoperation of the invention.

When the particle P, passes within the first embodiment of theseparating section, it passes between the annular ducts 109 as indicatedby phantom lines in FIG. 3 and is deflected past the grounded conductorrings 106 by the clean air shown in dashed lines in FIG. 3 issusingthrough the openings 111 on both sides of the rings 106. The particle Ppis now located within the side wall and is acted on by the electrostaticforce field F between the grids 101 and 102 and side wall 105. It willbe noted in FIG. 1 that side wall 105 is insulated from the rest of theduct 10 at I. Thus, as seen in FIG. 13, the force field F will exert aresultant force fon the particle Pp. The force fhas one componentfl.which is diametrically opposite to the force P of the gas stream on theparticle. The componentf serves to retard the movement of the particle Palong the path of movement P. The forcef also has a component f,generally perpendicular to the path of movement P. The component f, isdirected radially outward from the path of movement P so that theparticle P, will be deflected outwardly toward the nearest portion ofside wall 105. This deflection is seen by the phantom lines in FIG. 1.Thus, the particles Pp will be deflected toward and collected on theinside surface 107 of side wall 105 in an outwardly flaring funnelshaped pattern. It will also be noted that the contra component f,. isthe major component of force fand the radial componentf, is the minorcomponent since the major part of the electrostatic force is used toslow down the particle so that it can be easily separated.

The distance L between the entry grid 101 and exit grid 102 may bevaried for the optimum separating efficiency. The distance L will dependon the diameter d of duct 10. Also, the potential difference between theentry and exit grids 101 and 102 and between the exit grid 102 and sidewall 105 may be varied to obtain maximum separation. It has been found,however, that a potential difference of 10,000 to 40,000 volts betweengrids 101 and 102 and between grid 102 and side wall 105 is sufficient.In practice, the potential difference is maintained as high as possiblewithout arcing. Of course it is to be understood that additionalsections 100 may be placed downstream of the section 100 illustrated toremove any particles from the gas stream that were not removed in thefirst section 100. Also, it will be noted that the electrostatic field Facts as a means for charging the particles P Thus, in some cases, thecorona discharge unit 12 may not be necessary where the particles willbe both charged with a charge of a polarity like grid 102, especially ifthe grid 101 is grounded, and separated from the gas stream after thecharge is imposed thereon.

When the cleaning mechanism 130 is used, the cylinder 131 is positionedto align one of the side walls 105 in the duct so that the particulatematter will be collected on the inside surface 107 of the aligned wall105. When the surface 107 of the aligned side wall 105 becomes coatedwith particulate matter to such an extent to affect the collectingefficiency thereof, the cylinder 131 is indexed by motor 134 until thenext side wall 105 is aligned with the duct 10 without interrupting theoperating of the section 100. When the coated side wall 105 is indexedto the cleaning brush 135, it is rotated by motor 136 and moved alongcarriage 138 to clean the side wall 105. Thus, it will be seen that theoperation is continuous.

In the operation of the second embodiment 200 of the separating section,the particles P pass the grid 201 in the same manner as described forgrid 101. The electrostatic force field F will exert the force fon theparticle P with the componentf, diametrically opposite the force Fthereon in the same manner as the force f,. of field F to retard themovement of the particle along-path P. The component f,, of force fasseen in FIG. 7 corresponds to force f, of field F in that it is directednormal to path P, however, it is different in that it is directed onlytoward the collection member 230 completely across the crosssection ofthe side wall 205. Thus, the particles within section 200 will bedeflected toward the collection member 230 across the entire crosssection of side wall 205 as indicated by phantom lines in FIG. 7.

When the collection member 230 has been sufficiently coated with thecollected particulate matter to lose its collecting efficiency, themember 230 is indexed to place a clean portion thereof in registrationwith the opening 206 in the side wall 205 to provide for continuousoperation while the cleaning member 232 cleans the coated portion ofmember 230. While only one member 230 is illustrated, it is to beunderstood that additional members 230 may be positioned around the sidewall 205 and in combination with additional members 225 on exit grid 202on that side of the passage 214 of side wall 205 opposite the additionalcollection members 230 to also separate the particles from the gasstream. It is also to be understood that different types of cleaningmechanisms and collection members may be used in lieu of thoseillustrated.

The operation of the modification 300 of the second embodiment of theinvention is virtually the same as the second embodiment thereof.Because the angles a and B for grids 301 and 302 are selected in therange of 45 to 90, the componentf, of force fretards movement of theparticles Pp while the component f,, of force fdeflects all of theparticles toward the collecting member 330 as indicated by phantom linesin FIG. 9. It will be noted that the plane of the charged surfaces ofgrids 301 and 302 define the included acute angles a and ,8 with theplane of the surface of the collection member 330 exposed to the gasstream and intersect the plane of the collection member along a linenormal to the longitudinal centerline of the member 330 which isparallel to the path P along which the gas stream passes. Also, the exitgrid 302 extends over the member 330 from the downstream end thereof.

As seen in FIG. 10, the particle Pp passes through the entry grid 401 ofthe third embodiment 400 of the separating section in the same manner asit passes grid 101 in the first embodiment 100. Because the side wall405 is grounded, the particles are subjected to the same forces f, and fas they move between grids 401 and 402,, as described for the firstembodiment of the separating section to be collected on side wall 405between grids 401 and 402,,, the side wall 405 being insulated from therest of the duct 10 at l.

[f the particle Pp is not separated in the field F between grids 401 and402 it passes downstream of grid 402,,. Unlike the first embodiment 100wherein the charged particle would be speeded up when it passeddownstream of the exit grid 102, however, it encounters theelectrostatic field F to exert the force f thereon with the contracomponent f,. and the radial componentf, seen in FIG. 10 which causesthe particle to continue to slow down while at the same time continue tobe deflected outwardly toward the grounded side wall 405 between grids402,, and 402,,. It will be noted that side wall 405 is also insulatedfrom the rest of duct 10 at the insulators l. The electrostatic field F,will be generated as long as the potential on grid 402,, is greater thanthat on grid 402,, and of the same polarity as grid 402,, and the chargeon the particles. The side wall 405' is charged with a polarity oppositeto that of grid 402,, here shown as grounded, to continue to attract theparticle theretoward and collect same thereon.

Likewise, if the particle Pp is not separated from the gas stream in thefield F, between grids 402,, and 402,,, it passes downstream of grid402,, to be subjected to the electrostatic field F between grids 402,,and 402,. Because the potential imposed on grid 402,. is always greaterthan that on grid 402,, and of the same polarity as the potential ongrid 402,, and the particles Pp, the forcef, exerted on the particle Pphas a componentf," contra to the flow of the gas stream and a componentf, in a radial direction with respect to the side wall 405" and normalto the path P. The side wall 405" is also grounded and insulated fromthe rest of duct 10 at l"v This insures that the particles will continueto be attracted toward the side wall 405'.

It is to be fuurther understood that while only three grids 402 areillustrated in FIG. 10, additional grids 402 may be placed downstream ofthose illustrated with "each having a higher potential imposed thereonthan the adjacent upstream grid 402 with the same polarity as theadjacent upstream grid 402 to generate a repulsive force field. Whiledifferent voltages V,, V and V may be used depending on the particularkind of particles to be separated and the desired separating efficiency,one set of suggested voltages is 10,000 volts f0 voltage V,, 20,000volts for voltage V and 30,000 volts for voltage V,,. As discussed withthe first embodiment 100 of the separating section, the distances L, Land L" between grids 401 and 402,402, may be varied for maximumseparating efficiency and will depend on the diameter d of the passagedefined by side walls 405, 405 and 405'.

In some applications, the grid 401 may not be necessary with all of theseparation taking place between the grids 402,,402,. If such is thecase, grid 401 can be eliminated and the side wall 405 need not begrounded.

It is also to be understood that in some instances the side walls 405,405 and 405" may not need be oppositely charged or grounded. This isbecause the self repulsion forces between the particles will cause themto drift toward the side walls as they are slowed down by the contraforces from force fields F, F and F of the duct wall between the firstand second grids; imposing an electrical potential ofa prescribed valueon the second grid with the same polarity as that on the particles togenerate an electrostatic repulsive The difference between the operationof a precipita- 5 force field between the second grid, the first gridtor using a series of separating sections 100 and the and the duct wallwhich exerts a first component of separating section 400 is that eachtime a particle force on the particles as they pass between the firstmoves downstream of an exit grid 102, it is accelerated and second gridsopposite to the direction of move until it passesthe next downstreamentry grid 101 ment of the gas stream along the prescribed path whereasa retarding force is constantly exerted on'th'e l and exerts a secondcomponent of force on the parparticle from the time it enters thesection'400 until the ticles generally toward the duct wall and normalto time it leaves the section. This results in reducing 'the themovement of the gas stream to slow the movesection 400 to a minimum bymaximizing the separatment of the particles with the gas stream anddeing efficiency thereof. fleet the particles to the duct wall forcollection;

With the invention disclosed herein, the less turbul and, lent the flowof the gas stream through the duct the preventing the collection of thecharged particles on better the separating efficiency. Thus, thesections'of the upstream side of the grounded first grid so that theinvention are designed to introduce a'minimum of the particles arecollected only on the duct wall. turbulence into the gas stream unlikethose prior art 2. Themethod of claim 1 wherein the step ofpreprecipitators which use turbulence to mechanically venting thecollection of the charged particles on the slow down the particles. Thisresults in maintaining the upstream side of the grounded first gridincludes elecpumping power necessary to force the gas stream tricallyshielding the upstream. side of the first grid. through the precipitatorat a minimum. 3. The method of claim 2 wherein the step of pre- The useof grid 500 in lieu of the grids previously ilventing the collection ofcharged particles on the uplustrated does not materially change theoperation as stream side of the grounded first grid further includesabove described. It will be noted that the coating 505 directing asecondary stream. of a gaseous medium may be necessary when grid 500 isused in lieu of the without charged particles therein around theperipheral entry grids 101, 201, 301 or 401 to prevent collection edgesof the first grid to cause the gas stream with the of the particlesthereon. charged particles therein to bypass the grounded first Whilespecific embodiments of the invention have grid without the chargedparticles being collected on been disclosed herein, it is to beunderstood that full the first grid. use may be made of modifications,substitutions and 4. A method of separating charged particles from aequivalents without departing from the scope of the ingas streamincluding the steps of: ventive t, 3 moving the gas stream with thecharged particles en- TABLE I GASEOUS POLLUTANT To BE CONVERTING ME-PARTICULATE PRODUCT DIUM CoNvERTED MEDlUM STATE PRODUCT STATE SulfurDioxide Ammonia Gus Ammonium Sulfate Solid (S01) (NHH) l( il-z il SulfurDioxide Calcium Oxide Solid Calcium Sulfate Solid (S02) (CaO) (CaSO,)Sulfur Dioxide Manganese Di- Solid Manganese Sul- Solid (SO. oxide (MnOfate (MnSO,) Nitrogen Dioxide Cyclic Olefin Gas Aerosol Liquid/Gas (NO-l Group Nitric Oxide Air/Ox gen Gas Nitrogen Di- Gas (NO) (O2) oxide(N02) Carbon Monoxide Air/Oxygen Gas None 1 (0 Carbon Monoxide LeadChloride Solid Lead Solid (CO) (PbCl H2O) We claim: trained thereinalong a prescribed path within a tu- 1. A method of separating chargedparticles from a b la d t; gas stream including the steps of:positioning a plurality of first open grids so as to inmoving lhC gasstream with [llC charged particles entcrsect said prescribed path spacedfrom each trained therein along a prescribed path through a other b a ibd di tubular duct; imposing an electrical potential ofa prescribed valuepositioning a first open grid within the tubular duct on said mostupstream first open grid with the same so that the first grid extendsgenerally transversely polarity as that of the charge on said particles;

across the prescribed path; imposing an electrical potential on theremaining first positioning a second open grid within the tubular gridsof the same polarity as the charge on said parduct a prescribed distancedownstream of the first ticles, the charge on each of said remainingfirst grid so that the second grid extends generally transversely acrossthe prescribed path; electrically grounding the first grid and thatportion grids having a value a predetermined amount greater than thecharge on the next adjacent upstream first grid;

positioning an additional second open grid so as to intersect saidprescribed path and spaced upstream from said most upstream first opengrid.

electrically grounding said additional second open grid and said tubularduct between adjacent open grids; and,

electrically shielding the upstream side of said second open grid toprevent the collection of the charged particles thereon so that anelectrostatic repulsive force field is generated between adjacent gridsand the duct wall therebetween which exerts a first component of forceon the particles as they pass between adjacent grids opposite to thedirection of movement of the gas stream along the prescribed path andexerts a second component of force on the particles generally toward theduct wall and normal to the prescribed path to slow the movement of theparticles with the gas stream and de' fleet the particles to the ductwall for collection.

5. The method of claim 4 further including the step of directing a flowof a gaseous medium without charged particles therein about theperipheral surfaces of said second open grid and generally parallel tothe prescribed path to cause the gas stream with the charged particlesentrained therein to pass by the second open grid without particlesbeing collected thereon.

6. The method of claim 5 further including the step of imposing a chargeon the particles entrained in the gas stream upstream of said secondopen grid of the same polarity as the charge on said first grids.

7. The method of claim 6 further including the step of injecting aconverting medium into the gas stream upstream of the point at which theelectrical charge is imposed on the particles therein to convert gaseouspollutants in the gas stream into particulate matter for acceptance ofan electrical charge thereon.

1. A METHOD OF SEPARATING CHARGED PARTICLES FROM A GAS STREAM INCLUDINGTHE STEPS OF: MOVING THE GAS STREAM WITH THE CHARGED PRTICLES ENTRAINEDTHEREIN ALONG A PRESCRIBED PATH THROUGH A TUBULAR DUCT POSITIONING AFIRST OPEN GRID WITHIN THE TUBULAR DUCT SO THAT THE FIRST GRID EXTENDSGENERALLY TRANSVERSELY ACROSS THE PRESCRIBED PATH, POSITIONING A SECONDOPEN GRID WITHIN THE TUBULAR DUCT A PRESCRIBED DISTANCE DOWNSTREAM OFTHE FIRST GRID SO THAT THE SECOND GRID EXTENDS GENERALLY TRANSVERSELYACROSS THE PRESCRIBED PATH, ELECTRICALLY GROUNDING THE FIRST AND THATPORTION OF THE DUCT WALL BETWEEN THE FIRST AND SECOND GRIDS, IMPOSING ANELECTRICAL POTENTIAL OF A PRESCRIBED VALUE ON THE SECOND GRID WITH THESAME POLARITY AS THAT ON THE PARTICLES
 2. The method of claim 1 whereinthe step of preventing the collection of the charged particles on theupstream side of the grounded first grid includes electrically shieldingthe upstream side of the first grid.
 3. The method of claim 2 whereinthe step of preventing the collection of charged particles on theupstream side of the grounded first grid further includes directing asecondary stream of a gaseous medium without charged particles thereinaround the peripheral edges of the first grid to cause the gas streamwith the charged particles therein to bypass the grounded first gridwithout the charged particles being collected on the first grid.
 4. Amethod of separating charged particles from a gas stream including thesteps of: moving the gas stream with the charged particles entrainedtherein along a prescribed path within a tubular duct; positioning aplurality of first open grids so as to intersect said prescribed pathspaced from each other by a prescribed distance; imposing an electricalpotential of a prescribed value on said most upstream first open gridwith the same polarity as that of the charge on said particles; imposingan electrical potential on the remaining first grids of the samepolarity as the charge on said particles, the charge on each of saidremaining first grids having a value a predetermined amount greater thanthe charge on the next adjacent upstream first grid; positioning anadditional second open grid so as to intersect said prescribed path andspaced upstream from said most upstream first open grid, electricallygrounding said additional second open grid and said tubular duct betweenadjacent open grids; and, electrically shielding the upstream side ofsaid second open grid to prevent the collection of the charged particlesthereon so that an electrostatic repulsive force field is generatedbetween adjacent grids and the duct wall therebetween which exerts afirst component of force on the particles as they pass between adjacentgrids opposite to the direction of movement of the gas stream along theprescribed path and exerts a second component of force on the particlesgenerally toward the duct wall and normal to the prescribed path to slowthe movement of the particles with the gas stream and deflect theparticles to the duct wall for collection.
 5. The method of claim 4further including the step of directing a flow of a gaseous mediumwithout charged particles therein about the peripheral surfaces of saidsecond open grid and generally parallel to the prescribed path to causethe gas stream with the charged particles entrained therein to pass bythe second open grid without particles being collected thereon.
 6. Themethod of claim 5 further including the step of imposing a charge on theparticles entrained in the gas stream upstream of said second open gridof the same polarity as the charge on said first grids.
 7. The method ofclaim 6 further including the step of injecting a conveRting medium intothe gas stream upstream of the point at which the electrical charge isimposed on the particles therein to convert gaseous pollutants in thegas stream into particulate matter for acceptance of an electricalcharge thereon.